Abstract
Recently the background noise level of cars when driving on both rough and
smooth roads has been dramatically improved. As a result, tire cavity noise has become more
noticeable. However, it is very difficult to improve this phenomenon, because its resonance
has a very sharp peak. This resonance transfers easily through every part of the car, and is
difficult to control in the body structure. It is necessary to improve this phenomenon at the
source, i.e., the tire and wheel assembly.
This article describes a countermeasure applied to the wheel. This countermeasure should be
included in design guidelines for designers in the early stages of design. As the first step, a
bench test method was established for analyzing the mechanism of this phenomenon. This
method involved directly exciting the acoustic modes of the tire cavity by inserting a speaker
into the tire wheel assembly. This method has better FRF data reliability than tire hammering
tests, which do not produce reliable data because rubber properties are not linear.
The acoustic coupling of the wheel vibration mode was therefore analyzed using the new
method. It was determined that a torsional mode of the disk is excited by an acoustic mode of
the tire cavity. The input force determined by the acoustic cavity mode has a large impact on
which wheel mode is excited. As an example, the 1st order wheel resonance (this is not the
torsional mode of the disk) was tuned to the same frequency as the tire cavity resonance, but
the torsional mode of the disk was still dominant.
Finally it was found that disk torsional stiffness is an important design factor. If the wheel
vibration caused by the acoustic cavity mode is low, then the force that transfers to the
suspension is also low. This theory was proved using three different wheels with a disk
torsional stiffness of 800, 1000, and 1200 kNm/rad (measured by a method devised by the
authors). The effect of disk torsional stiffness was then verified on a vehicle in actual driving
conditions.
Keywords - wheel, tire, acoustic, cavity, coupling mode